We have discovered that at least three histone classes are resolvable into subfractions (compounds) that are synthesized at different stages of embryogenesis. The biological significance of this phenomenon will be probed by studies of: (a) protein structure differences between the histone components by a comparison of peptides produced by various agents; (b) longevity and coordination of synthesis among the histone components, by isotope incorporation measurements; (c) the location of the various histone components within the embryo by i) fractionation of different cell types and analysis of their histones and ii) immunofluorescence of squashed or sectioned embryos; (d) the arrangement of the histone components within chromatin by enzymic dissection of the chromatin and (e) the effects of the various histone components on chromatin structure as revealed by nuclease susceptibility of chromatin preparations differing in their histone components.